Receptor internalization is an adaptation mechanism
shown to occur in response to large agonist doses. To
date, there has not been a method for detecting
internalization in vivo, although it may affect
functional imaging signals. In this study, we use
simultaneous PET/fMR imaging and graded doses of a D2
agonist in order to investigate D2 receptor
internalization. We propose a model that combines fMRI
timecourses with dynamic receptor occupancies measured
by PET to derive an in vivo index of dopamine receptor
internalization non-invasively.

Brain mapping of task-associated changes in metabolism
with PET has been accomplished in the past by
subtracting scans acquired during two distinct static
states. Here we show that PET can provide truly dynamic
information on cerebral metabolism using concepts common
to fMRI. Using 2-[18F]-fluoro-deoxyglucose (FDG), we
show that quantitative glucose utilization changes
during multiple visual stimuli can be determined using
FDG constant infusion in a single-imaging experiment.
This functional PET (fPET-FDG) method can be
accomplished simultaneously with fMRI (BOLD and ASL) and
thus enables the first direct comparisons in time, space
and magnitude of glucose utilization, hemodynamics and
oxygen consumption.

13:54

0383.

Brain connectivity mapping
based on Positron Emission Tomography (PET) in comparison to
fMRI using combined PET/MR

Brain connectivity is mainly derived from fMRI data.
Here we present an approach to visualize functional and
metabolic networks in the rat brain using combined PET
and MR imaging. Three different PET tracers, mapping
glucose, perfusion and serotonin transporter
contributions to functional connectivity are compared
with fMRI. Our results reveal that fundamental
information about functional and metabolic brain
networks is encoded in dynamic and static PET data. This
opens the arena for quantitative PET based functional
connectivity methods that can be complemented with fMRI.

14:06

0384.

Correlations between PET
and Resting State fMRI of Default Network using Simultaneous
PET/MR: Preliminary Results

Yu-Shin Ding1,2, Adriana Di Martino3,
Bangbin Chen4, Krishna Somandepalli3,
Christopher Glielmi5, Kritika Nayar3,
and Francisco X Castellanos3,61Radiology, New York University School of
Medicine, New York, NY, United States,2Psychiatry,
New York University School of Medicine, New York, NY,
United States,3Child
and Adolescent Psychiatry, New York University School of
Medicine, NY, United States,4National
Taiwan University Hospital, Taiwan,5Siemens
Healthcare, NY, United States,6Neuroscience
and Physiology, New York University School of Medicine,
NY, United States

Our results demonstrated the feasibility of correlating
FDG metabolism and resting-state fMRI data acquired
simultaneously via a combined PET/MR on healthy
participants. We showed that PCC-based intrinsic
functional connectivity with the anterior node of the
default network is positively related to glucose
consumption, which in turn is related to fluctuations in
the BOLD signal specific to gray matter regions. The
fMRI signals are indirect measures of neuronal activity;
thus, the ability to simultaneously interrogate
metabolism and fMRI indices of brain function in the
same temporal and spatial frames of reference provides
greater insights into whole brain network organization.

To investigate the neural correlate of fMRI
resting-state networks (RSNs), we recorded and analyzed
large-scale ECoG data from macaques during eyes-closed
wakefulness, sleep, and two anesthetic regimes. A
data-driven analysis on co-variations of spontaneous
power fluctuations revealed 8 spatial patterns that
corresponded closely to previously reported RSNs. These
patterns were similar across spectral frequency bands
and behavioral conditions. We conclude that fMRI RSNs
reflect the spatial organization of spontaneous
broadband neural activity, which appears to be a core
aspect of the brain’s physiology that is preserved
across various states of consciousness.

Han Yuan1, Lei Ding1,2, Min Zhu2,
and Jerzy Bodurka1,31Laureate Institute for Brain Research,
Tulsa, OK, United States,2School
of Electrical and Computer Engineering, University of
Oklahoma, Norman, OK, United States,3College
of Engineering, University of Oklahoma, Norman, OK,
United States

We developed a method to reconstruct the resting state
networks (RSNs) from high-resolution EEG data. We
combined electrophysiological source imaging and
independent component analysis to obtain cortical
distributions of eight RSNs from temporal independent
EEG microstates. We further compared both spatial and
temporal similarities of EEG-derived RSNs and
BOLD-fMRI-derived RSNs from simultaneously acquired
data. We found a high spatial similarity and temporal
correlations among all eight RSNs independently
identified from multimodal data. Results demonstrate the
intrinsic connection between fast neuronal activity and
slow hemodynamics fluctuation, and also show the utility
of EEG in studying resting brain networks.

Simultaneous PET/fMRI offers the unique opportunity to
relate neurochemical events to the functional changes
underlying neural activity. In this study, we present
simultaneous PET/fMRI study with pharmacological
challenges given to nonhuman primates to determine the
relationship between opioid receptor occupancy, dopamine
release, and changes in CBV. CBV-fMRI shows
dose-response to opioid agonist challenges. PET and fMRI
demonstrated concurrent signal changes overlapping in
the basal forebrain, such as the caudate, putamen, and
nucleus accumbens (NAc). In addition, the temporal
response of dopamine release matches a fast CBV decrease
in the NAc, while other brain regions show a slow CBV
increase comparable to the temporal dynamic of opioid
receptor binding.

MRS measurements of the primary inhibitory
neurotransmitter, GABA, and MRI measurements of CBF,
fractional gray matter volume, and arterial arrival time
(AAT) are recorded in human visual cortex from adult
male volunteers. The primary finding is that occipital
GABA derived from J-edited MEGA-PRESS inversely
correlates with CBF in the same region. This finding
provides some physiological basis for the reported
inverse relationships between BOLD responses and GABA. A
secondary finding is that AAT does not correlate
strongly with GABA, but failure to account for AAT in
ASL measurements can reduce or eliminate the
detectability of CBF-GABA relationships.

This study demonstrates focused ultrasound
co-administrated with microbubbles can modulate local
brain activities. Focused ultrasound with acoustic
pressures of 0.3 MPa produced reliable and reversible
brain modulation. This present study proposed a novel
non-invasive, reversible and localized brain modulated
method which is suitable for a variety of
neurophysiological experiments and clinical
applications.